Process of forming wearing-surfaces for asphalt pavements.



UNITED STATES PATENT OFFICE.

DANIEL P. MULLEN, OF WASHINGTON, DISTRlCT OF COLUMBIA.

PROCESS OF FORMING WEARING-SURFACES FOR ASPHALT PAVEMENTS.

SPECIFICATION forming part of Letters Patent No. 721,906, dated March 3, 1903. Application filed October 6, 1902. Serial lie-126,231. (No specimens.)

To all whom, it may concern.-

Be it known that I, DANIEL P. MULLEN, a citizen of the United States, residing at Washington, District of Columbia, have invented certain new and usefulImprovements in Processes of Forming earing-Surfaces for Asphalt Pavements, of which the following is a specification.

This invention relates to a process for forming a wearing-surface for asphalt pavements, and particularly to an improved method of mixingbroken stone and asphalt to form a wearing-surface impervious to moisture and possessing a smooth, even, and gritty surface in use.

The invention has for an object to combine with the asphalt forming the wearing-surface small stones or grit separately coated with asphalt cement, so that when introduced into the main body of the asphalt they will firmly adhere thereto and become an integral part of the wearing-surface.

Other and further objects and advantages of the invention will be hereinafter set forth and the novel features thereof defined by the appended claims.

Asphalt pavements have been laid for many years past in various compositions; but heretofore it has not been practical to produce a pavement that would combine the merits of being impervious to water, not susceptible to atmospheric influences, and at the same time have sufficient body, grit, and grip to prevent its polishing on the surface, cracking, pushing, or what is commonly known in the art as creeping. These defects are essentially due to the imperfection in the wearingsurface of the asphalt, and the present invention presents a wearing-surface adapted to remove the objections heretofore existing. This Wearing-surface may be laid upon any desired basefor instance, the foundation ordinarily used, which is covered by a binder, upon which the Wearing-surface is applied. The asphalt or bitumen used in my improved surfacemay be any of the standard grades now in use, which are softened to the desired extent for mixing by the use of oil or any wellknown ingredient for that purpose. These materials, combined with other ingredients,

as now used in standard asphalt pavements, are mixed in the usual way and proportions suitable to the traffic and climatic conditions to which the pavement will be subjected. When this mixture is thoroughly compounded into the ordinary condition for use, my improvement consists in adding theretoan egual amount in bulk of crushed pebbles,s tone, or grit, free from dust or dirt and of a size preferably not larger than three-eighths of an inch or smaller than one-eighth of an inch, which has been previopsly heated to a temperature somewhat ldwejr than tli'bitnminqns mixture and then separately treated with a slight coatihg of bituminous cement, similar to that used for the binding course, but not sufficient to add any bitumen to the asphalt mixture nor to remove any therefrom, but enough to properly coat each of the fine stones, so as to insure of its becoming a permanent integral part of the mixture. This independent complete coating of the stone with a slight covering of bituminous cement secures a positive adhesion between the particles of the stone and the body of the asphalt into which they are subsequently mixed and prevents the absorption by the stone of the liquid hydrocarbons present in the asphalt, thus deteriorating the quality thereof, as the independent complete coating fills the pores of the stone and presents a cementing-surface, by which compact adhesion is secured. These small stones after being separately coated are added to the previously thoroughly incorporated asphalt mixture and compose substantially fifty percent. ofthe same, although a greater or less proportion may be used to provide pavements for different conditions of service. When the whole mixture is completed, it will be found that the small stones are distributed thoughout the mass with a sufficient amount of the bituminous mixture surrounding each particle to bind it to another particle. It is not my intention to have the particles of stone come in direct contact with each other, but to displace sufiicient of the bituminous mixture to give place tothe stone added without causing said mixture to lose any of its binding or resisting qualities. This provides a pavement which when laid is firm and has sufficient grip and grit to hold it in place, thus preventing pushing or creeping and provides a smooth even surface with sufficient gritty matter at the point of Wear to ICO prevent polishing and give a firm foothold for horses. It will also be obvious that my improved wearing-surface is impervious to moisture and not afiected by ordinary condi tions of heat,which prevents rotting and also the indentation or displacement of the surface by softening under the influence of a hot sun. The surface is also capable of re sisting heavy wheel trafiic, and the coated stone maintains a more intimate contact with the binder beneath, while the appearance thereof is attractive to the eye, as the stone presents a light color to the surface. As the bulk of the mixture constituting the Wearingsurface is increased one hundred per cent. by the addition of stone, which is less expensive than the asphalt, a saving of about eighty per cent. is effected and much better results produced.

The present invention is not confined to the use of any particular bitumen or asphalt or to any particular kind of stone incorporated therein, nor any especial foundation; but the essential feature by which the improved results are obtained is the fine stone coated separately from the mixture of asphalt and incorporated therewith after the asphalt mixture has been made. It is apparent that variations from the process herein set forth may be made, in that the body of fine stone need not be preliminarily heated and that the average size thereof may be in excess of three-eighths of an inch; but such variations produce an inferior product, and I therefore prefer the sizes mentioned and the independent preliminary coating of the stones.

Having described my invention and set forth its merits, what I claim, and desire to secure by Letters Patent, is

1. The process of compounding a composition for forming an asphalt wearing-surface consisting in completely and slightly coating a mass of fine stone, separately forming an asphalt mixture, and then thoroughly incorporating and mixing the coated stones with said asphalt mixture.

2. The process of compounding a composition for forming an asphalt wearing-surface consisting in completely and slightly coating with asphaltic cement a mass of previouslyheated small stones of not less than one-eighth of an inch in diameter or more than threeeighths of an inch, separately forming an asphalt mixture, and then thoroughly incorporating and mixing the coated stones with a substantially equal amount in bulk of said asphalt mixture.

In testimony whereof I aflix my signature in presence of two witnesses.

DANIEL P. MULLEN.

Witnesses:

FRANK A. HARRISON, WM. H. BARSTOVV. 

